how-to connect 1F cap to car without danger of draining it after 3-4weeks?

Currently I have 1F cap connected to my car battery directly (40A cable) and the problem is that it drains 100mA constantly. If I don't use my car for 3-4 weeks my battery is drained so much, that it wont start my car.
It's a diesel which needs a lot of juice at start for preheat and starter.

I was thinking of getting some kind of disconnecting circuit, but this cap creates quite a big sparks when connecting and I'm afrait that these sparks will fry regular 20A relay contacts.

You could use a power MOSFET in the cap's ground path that receives voltage to it's gate only when the accessory switch is on. Use several high-wattage 12v bulbs in parallel between the battery's + terminal and your capacitor.

There will be a high initial surge current, but the bulbs will rapidly heat up increasing their resistance and decreasing the charge rate. As the cap becomes charged, the voltage across the bulbs will decrease, so they will cool and their resistance will decrease.

It doesn't seem to me that a capacitor, unless defective, should NOT have any kind of continuous DC leakage current pass through it once it charges up to the battery voltage. I know that when using series connected caps to come up with a overall cap with a higher effective working voltage, they sometimes wire up a string of series 'equalizing' resistors in parallel with the caps, to make sure each individual cap has the same voltage across it, and that would result in a small continuous DC current draw through the resistor string. But that wouldn't apply for a 1F cap designed for a 12volt system, would it? Or might this 1F cap be made from say 4 4F 5 volt 'super caps' in series and there is a equilization resistor string being used? I have no idea how these super large car audio caps are constructed.

Anyone have any ideas why the poster is seeing a continuous DC leakage current through the cap?

Haven't you seen those fancy huge capacitors in car radio stores?
They have a current-hogging LED display of voltage.
Maybe the display can be connected to the car lights so it turns off when the lights are turned off.

Haven't you seen those fancy huge capacitors in car radio stores?
They have a current-hogging LED display of voltage.
Maybe the display can be connected to the car lights so it turns off when the lights are turned off.

Click to expand...

No, I've only seen brief pictures in magazines and didn't notice they were also light displays. That would explain a continous current drain. Can they be disconnected as LEDs serve such a silly purpose in this application?